I have Google Fi on a Pixel and my bill this month will be roughly $25.00. That's for unlimited voice and text, and a PAYG data plan. Since the Fi spends so much time on WiFi, and so little on 4G/LTE, the data that is being consumed is almost nothing so I pay almost nothing. Subtract $20.00 for helping a friend sign up for Fi, and my bill will be roughly $5.00 this month.
Looking at the new iPhones, I realize I'll be able to use AT&T or T-Mobile (or both) as my eSIM provider in the USA, but I'll also be able to buy their lowest voice and data plan, as I'll be able to use the Fi's data only SIM in the other slot. Basically with an eSIM I'll have the best option around, as I can flip flop between AT&T and T-Mobile based on coverage areas, and still have the Fi Sim connected to T-Mobile or Sprint (until they merge). When I go internationally, I'll activate a PAYG Truphone plan for voice and data, and use that.
Of course I could also just put my Fi phone and data SIM into the SIM card slot and then use any of the UK or EU mobile operators as the PAYG eSIM provider when I'm in that part of the world, and Truphone or Fi everywhere else
There's a really big play here for Google and Truphone in the global traveller market, as it really takes off after the iPhone turns on the eSIM for everyone. Already the dual SIM Pixel2 provides this type of benefit, but let's face it, with what Apple is doing, it will bring the idea of dual SIM, dual carrier, mainstream in the USA, as it has been a big deal in Asia for a while.
For people who spend most of their time connected to the cloud, or on conference calls without the need to dial a number, the dual SIM plan will be golden. As a VoIP user, I already make calls for the most part over IP via LTE or WiFi. With apps using the data plan and regular calls going over the mobile operator SIM in the Voice/DataFi SIM scenario, I can forward the calls to my mobile operator to deal with calls when I'm in lower speed, poorer coverage areas. But when I'm in full coverage or WiFi, the Google Fi line becomes primary.
Even more, I can use services like Dialpad, Telzio or other cloud telephony providers to be my published line and take advantage of their wider array native features over WiFi and LTE. While FI may not support WiFi calling given how I use a VoIP provider more than my cellphone provider number to make calls, it's no big deal.
With CPaaS services from SignalWIRE, Twilio, Plivo and Nexmo, I can create various messaging and voice functions tied to applications or workflows. With location based features it will be likely that I'll be able to toggle between the two SIM service providers and the trigger services on and off, further taking advantage of the WiFi or LTE/4G networks.
At the end of the day, the dual SIM approach will likely provide a means to save money, by eliminating the cost of a second phone, and providing power users to really be able to choose which network is best for them, where they are and for what they do versus the current one size fits all approach being sold by the mobile operators.
The dual SIM really does offer, Power To The People.....right now.